San Diego County voter turnout in the Nov. 5 election appears to have been the lowest for a presidential election in 20 years, reflecting a trend that primarily hurt Democrats on the national level.

That’s despite the fact that tens of thousands more people registered to vote around the county in that time.

Low turnout may have been a factor that helped doom a few local proposed tax measures, said San Diego State University professor Brian Adams, who studies local and state politics.

Some votes are still being counted, and the election will not be certified by county officials until next month. But available voter registration and turnout data from the county registrar offer clues to help explain the outcomes. Here’s what an analysis by The San Diego Union-Tribune found.

Voter registration was up, but turnout was down

Nearly 2 million people — or 1,983,767, to be precise — were registered to vote in San Diego County for the 2024 general election. That’s almost 35,000 more than were registered in 2020.

But county voter turnout appears to have been significantly lower this year than in the past two presidential elections. Only about 76% of voters cast a ballot this fall, based on Registrar of Voters estimates — compared to 84% four years ago and 82% in 2016.

Before the election, the county registrar had predicted that turnout would be more than 80%, an estimate the office bases on turnout from the previous two presidential elections.

“We have no insights beyond that and can’t speculate as to why one chooses to participate or not participate in any given election,” said spokesperson Antonia Hutzell in an email.

Since Republicans are typically more likely to always vote in elections, Adams believes the lower turnout may be the product of Democratic voters who simply didn’t show up to vote.

“They just weren’t inspired by the candidates, they weren’t interested in the election, they just decided not to vote,” Adams said.

Adams believes the lower turnout likely worked against local sales tax increase measures on the ballot, namely Measure E in San Diego city and Measure G countywide.

“That’s maybe where you’re seeing that lower turnout really hurt,” he said.

More county voters opted for Donald Trump than they did four years ago.

Democrats are still the dominant political party in the county overall. The percentage of county voters registered as Democrats rose to 41%, from 40% in 2020 — which is lower than Democrats’ statewide share of 46%.

Meanwhile, the percentage of voters who registered as Republican virtually remained the same, at about 28%. Statewide, about 25% of voters are registered Republicans.

Yet this year, with an estimated 5% of county ballots still remaining to be counted, election returns so far show 40% of county voters chose Trump — up from 37% four years ago.

Meanwhile 57% voted for Kamala Harris, compared to 60% who voted for Joe Biden four years ago.

Early statewide returns suggest that San Diego County voters were slightly more likely to vote for Trump than statewide voters overall. With about 9% of ballots statewide left to be counted, about 59% of statewide voters chose Harris and 38% Trump.

Political party preferences countywide didn’t change much from 2020. But most ZIP codes in the county became bluer.

A smaller share of San Diego County voters was registered under “no party preference” — 25%, down from 27% in 2020. Still, no-party-preference voters make up a larger share of the county’s electorate than statewide, where 22% chose that designation.

The share of county voters registered with small political parties — Green, Peace and Freedom, Independent or Libertarian — rose to about 7%, up one and a half percentage points.

Over the past two decades, San Diego County’s electorate has gone from Republican-dominated to predominantly Democratic, a trend that mirrors those of other urban and coastal areas.

Today Democrats have a voter registration advantage not just in the city of San Diego and in South County, but also extending north into Carlsbad, San Marcos and Escondido, as well as east into La Mesa and El Cajon.

It’s only in deep inland East County and far North County that registered voters remain solidly Republican, as well as in Coronado, Miramar, Rancho Santa Fe, parts of Escondido and Poway.

No ZIP codes that are home to more than 100 registered voters flipped from one party advantage to the other since 2020.

Rather, more ZIP codes somewhat deepened their partisan lean. Now 26 ZIP codes have a Republican advantage over Democrats of more than 10 percent of voters, while 56 ZIP codes have a similar Democratic advantage.

That compares with 23 ZIP codes for Republicans and 53 for Democrats in the last presidential election.

In total, 61 ZIP codes increased their share of registered Democrats by at least one percentage point from 2020, compared to 36 ZIP codes that did so for registered Republicans. In 16 other ZIP codes, the balance didn’t change.

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